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A Real-Time Look at Value-Based Decision Making

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All of us make many decisions every day. For most things, such as which jacket to wear or where to grab a cup of coffee, there’s usually no right answer, so we often decide using values rooted in our past experiences. Now, neuroscientists have identified the part of the mammalian brain that stores information essential to such value-based decision making.

Researchers zeroed in on this particular brain region, known as the retrosplenial cortex (RSC), by analyzing movies—including the clip shown about 32 seconds into this video—that captured in real time what goes on in the brains of mice as they make decisions. Each white circle is a neuron, and the flickers of light reflect their activity: the brighter the light, the more active the neuron at that point in time.

All told, the NIH-funded team, led by Ryoma Hattori and Takaki Komiyama, University of California at San Diego, La Jolla, made recordings of more than 45,000 neurons across six regions of the mouse brain [1]. Neural activity isn’t usually visible. But, in this case, researchers used mice that had been genetically engineered so that their neurons, when activated, expressed a protein that glowed.

Their system was also set up to encourage the mice to make value-based decisions, including choosing between two drinking tubes, each with a different probability of delivering water. During this decision-making process, the RSC proved to be the region of the brain where neurons persistently lit up, reflecting how the mouse evaluated one option over the other.

The new discovery, described in the journal Cell, comes as something of a surprise to neuroscientists because the RSC hadn’t previously been implicated in value-based decisions. To gather additional evidence, the researchers turned to optogenetics, a technique that enabled them to use light to inactivate neurons in the RSC’s of living animals. These studies confirmed that, with the RSC turned off, the mice couldn’t retrieve value information based on past experience.

The researchers note that the RSC is heavily interconnected with other key brain regions, including those involved in learning, memory, and controlling movement. This indicates that the RSC may be well situated to serve as a hub for storing value information, allowing it to be accessed and acted upon when it is needed.

The findings are yet another amazing example of how advances coming out of the NIH-led Brain Research through Advancing Innovative Neurotechnologies® (BRAIN) Initiative are revolutionizing our understanding of the brain. In the future, the team hopes to learn more about how the RSC stores this information and sends it to other parts of the brain. They note that it will also be important to explore how activity in this brain area may be altered in schizophrenia, dementia, substance abuse, and other conditions that may affect decision-making abilities. It will also be interesting to see how this develops during childhood and adolescence.

Reference:

[1] Area-Specificity and Plasticity of History-Dependent Value Coding During Learning. Hattori R, Danskin B, Babic Z, Mlynaryk N, Komiyama T. Cell. 2019 Jun 13;177(7):1858-1872.e15.

Links:

Brain Research through Advancing Innovative Neurotechnologies® (BRAIN) Initiative (NIH)

Komiyama Lab (UCSD, La Jolla)

NIH Support: National Institute of Neurological Disorders and Stroke; National Eye Institute; National Institute on Deafness and Other Communication Disorders


What a Memory Looks Like

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Engram Image
Credit: Stephanie Grella, Ramirez Group, Boston University

Your brain has the capacity to store a lifetime of memories, covering everything from the name of your first pet to your latest computer password. But what does a memory actually look like? Thanks to some very cool neuroscience, you are looking at one.

The physical manifestation of a memory, or engram, consists of clusters of brain cells active when a specific memory was formed. Your brain’s hippocampus plays an important role in storing and retrieving these memories. In this cross-section of a mouse hippocampus, imaged by the lab of NIH-supported neuroscientist Steve Ramirez, at Boston University, cells belonging to an engram are green, while blue indicates those not involved in forming the memory.

When a memory is recalled, the cells within an engram reactivate and turn on, to varying degrees, other neural circuits (e.g., sight, sound, smell, emotions) that were active when that memory was recorded. It’s not clear how these brain-wide connections are made. But it appears that engrams are the gatekeepers that mediate memory.

The story of this research dates back several years, when Ramirez helped develop a system that made it possible to image engrams by tagging cells in the mouse brain with fluorescent dyes. Using an innovative technology developed by other researchers, called optogenetics, Ramirez’s team then discovered it could shine light onto a collection of hippocampal neurons storing a specific memory and reactivate the sensation associated with the memory [1].

Ramirez has since gone on to show that, at least in mice, optogenetics can be used to trick the brain into creating a false memory [2]. From this work, he has also come to the interesting and somewhat troubling conclusion that the most accurate memories appear to be the ones that are never recalled. The reason: the mammalian brain edits—and slightly changes—memories whenever they are accessed.

All of the above suggested to Ramirez that, given its tremendous plasticity, the brain may possess the power to downplay a traumatic memory or to boost a pleasant recollection. Toward that end, Ramirez’s team is now using its mouse system to explore ways of suppressing one engram while enhancing another [3].

For Ramirez, though, the ultimate goal is to develop brain-wide maps that chart all of the neural networks involved in recording, storing, and retrieving memories. He recently was awarded an NIH Director’s Transformative Research Award to begin the process. Such maps will be invaluable in determining how stress affects memory, as well as what goes wrong in dementia and other devastating memory disorders.

References:

[1] Optogenetic stimulation of a hippocampal engram activates fear memory recall. Liu X, Ramirez S, Pang PT, Puryear CB, Govindarajan A, Deisseroth K, Tonegawa S. Nature. 2012 Mar 22;484(7394):381-385.

[2] Creating a false memory in the hippocampus. Ramirez S, Liu X, Lin PA, Suh J, Pignatelli M, Redondo RL, Ryan TJ, Tonegawa S. Science. 2013 Jul 26;341(6144):387-391.

[3] Artificially Enhancing and Suppressing Hippocampus-Mediated Memories. Chen BK, Murawski NJ, Cincotta C, McKissick O, Finkelstein A, Hamidi AB, Merfeld E, Doucette E, Grella SL, Shpokayte M, Zaki Y, Fortin A, Ramirez S. Curr Biol. 2019 Jun 3;29(11):1885-1894.

Links:

The Ramirez Group (Boston University, MA)

Ramirez Project Information (Common Fund/NIH)

NIH Director’s Early Independence Award (Common Fund)

NIH Director’s Transformative Research Award (Common Fund)

NIH Support: Common Fund


New Grants Explore Benefits of Music on Health

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It’s not every day you get to perform with one of the finest voices on the planet. What an honor it was to join renowned opera singer Renée Fleming back in May for a rendition of “How Can I Keep from Singing?” at the NIH’s J. Edward Rall Cultural Lecture. Yet our duet was so much more. Between the song’s timeless message and Renée’s matchless soprano, the music filled me with a profound sense of joy, like being briefly lifted outside myself into a place of beauty and well-being. How does that happen?

Indeed, the benefits of music for human health and well-being have long been recognized. But biomedical science still has a quite limited understanding of music’s mechanisms of action in the brain, as well as its potential to ease symptoms of an array of disorders including Parkinson’s disease, stroke, and post-traumatic stress disorder (PTSD). In a major step toward using rigorous science to realize music’s potential for improving human health, NIH has just awarded $20 million over five years to support the first research projects of the Sound Health initiative. Launched a couple of years ago, Sound Health is a partnership between NIH and the John F. Kennedy Center for the Performing Arts, in association with the National Endowment for the Arts.

With support from 10 NIH institutes and centers, the Sound Health awardees will, among other things, study how music might improve the motor skills of people with Parkinson’s disease. Previous research has shown that the beat of a metronome can steady the gait of someone with Parkinson’s disease, but more research is needed to determine exactly why that happens.

Other fascinating areas to be explored by the Sound Health awardees include:

• Assessing how active music interventions, often called music therapies, affect multiple biomarkers that correlate with improvement in health status. The aim is to provide a more holistic understanding of how such interventions serve to ease cancer-related stress and possibly even improve immune function.

• Investigating the effects of music on the developing brain of infants as they learn to talk. Such work may be especially helpful for youngsters at high risk for speech and language disorders.

• Studying synchronization of musical rhythm as part of social development. This research will look at how this process is disrupted in children with autism spectrum disorder, possibly suggesting ways of developing music-based interventions to improve communication.

• Examining the memory-related impacts of repeated exposures to a certain song or musical phrase, including those “earworms” that get “stuck” in our heads. This work might tell us more about how music sometimes serves as a cue for retrieving associated memories, even in people whose memory skills are impaired by Alzheimer’s disease or other cognitive disorders.

• Tracing the developmental timeline—from childhood to adulthood—of how music shapes the brain. This will include studying how musical training at different points on that timeline may influence attention span, executive function, social/emotional functioning, and language skills.

We are fortunate to live in an exceptional time of discovery in neuroscience, as well as an extraordinary era of creativity in music. These Sound Health grants represent just the beginning of what I hope will be a long and productive partnership that brings these creative fields together. I am convinced that the power of science holds tremendous promise for improving the effectiveness of music-based interventions, and expanding their reach to improve the health and well-being of people suffering from a wide variety of conditions.

Links:

The Soprano and the Scientist: A Conversation About Music and Medicine, (National Public Radio, June 2, 2017)

NIH Workshop on Music and Health, January 2017

Sound Health (NIH)

NIH Support: National Center for Complementary and Integrative Health; National Eye Institute; National Institute on Aging; National Institute on Alcohol Abuse and Alcoholism; National Institute on Deafness and Other Communication Disorders; National Institute of Mental Health; National Institute of Neurological Disorders and Stroke; National Institute of Nursing Research; Office of Behavioral and Social Sciences Research; Office of the Director


New Study Points to Targetable Protective Factor in Alzheimer’s Disease

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Credit: gettyimages/Creatista

If you’ve spent time with individuals affected with Alzheimer’s disease (AD), you might have noticed that some people lose their memory and other cognitive skills more slowly than others. Why is that? New findings indicate that at least part of the answer may lie in differences in their immune responses.

Researchers have now found that slower loss of cognitive skills in people with AD correlates with higher levels of a protein that helps immune cells clear plaque-like cellular debris from the brain [1]. The efficiency of this clean-up process in the brain can be measured via fragments of the protein that shed into the cerebrospinal fluid (CSF). This suggests that the protein, called TREM2, and the immune system as a whole, may be promising targets to help fight Alzheimer’s disease.

The findings come from an international research team led by Michael Ewers, Institute for Stroke and Dementia Research, Ludwig-Maximilians-Universität München, Germany, and Christian Haass, Ludwig-Maximilians-Universität München, Germany and German Center for Neurodegenerative Diseases. The researchers got interested in TREM2 following the discovery several years ago that people carrying rare genetic variants for the protein were two to three times more likely to develop AD late in life.

Not much was previously known about TREM2, so this finding from a genome wide association study (GWAS) was a surprise. In the brain, it turns out that TREM2 proteins are primarily made by microglia. These scavenging immune cells help to keep the brain healthy, acting as a clean-up crew that clears cellular debris, including the plaque-like amyloid-beta that is a hallmark of AD.

In subsequent studies, Haass and colleagues showed in mouse models of AD that TREM2 helps to shift microglia into high gear for clearing amyloid plaques [2]. This animal work and that of others helped to strengthen the case that TREM2 may play an important role in AD. But what did these data mean for people with this devastating condition?

There had been some hints of a connection between TREM2 and the progression of AD in humans. In the study published in Science Translational Medicine, the researchers took a deeper look by taking advantage of the NIH-funded Alzheimer’s Disease Neuroimaging Initiative (ADNI).

ADNI began more than a decade ago to develop methods for early AD detection, intervention, and treatment. The initiative makes all its data freely available to AD researchers all around the world. That allowed Ewers, Haass, and colleagues to focus their attention on 385 older ADNI participants, both with and without AD, who had been followed for an average of four years.

Their primary hypothesis was that individuals with AD and evidence of higher TREM2 levels at the outset of the study would show over the years less change in their cognitive abilities and in the volume of their hippocampus, a portion of the brain important for learning and memory. And, indeed, that’s exactly what they found.

In individuals with comparable AD, whether mild cognitive impairment or dementia, those having higher levels of a TREM2 fragment in their CSF showed a slower decline in memory. Those with evidence of a higher ratio of TREM2 relative to the tau protein in their CSF also progressed more slowly from normal cognition to early signs of AD or from mild cognitive impairment to full-blown dementia.

While it’s important to note that correlation isn’t causation, the findings suggest that treatments designed to boost TREM2 and the activation of microglia in the brain might hold promise for slowing the progression of AD in people. The challenge will be to determine when and how to target TREM2, and a great deal of research is now underway to make these discoveries.

Since its launch more than a decade ago, ADNI has made many important contributions to AD research. This new study is yet another fine example that should come as encouraging news to people with AD and their families.

References:

[1] Increased soluble TREM2 in cerebrospinal fluid is associated with reduced cognitive and clinical decline in Alzheimer’s disease. Ewers M, Franzmeier N, Suárez-Calvet M, Morenas-Rodriguez E, Caballero MAA, Kleinberger G, Piccio L, Cruchaga C, Deming Y, Dichgans M, Trojanowski JQ, Shaw LM, Weiner MW, Haass C; Alzheimer’s Disease Neuroimaging Initiative. Sci Transl Med. 2019 Aug 28;11(507).

[2] Loss of TREM2 function increases amyloid seeding but reduces plaque-associated ApoE. Parhizkar S, Arzberger T, Brendel M, Kleinberger G, Deussing M, Focke C, Nuscher B, Xiong M, Ghasemigharagoz A, Katzmarski N, Krasemann S, Lichtenthaler SF, Müller SA, Colombo A, Monasor LS, Tahirovic S, Herms J, Willem M, Pettkus N, Butovsky O, Bartenstein P, Edbauer D, Rominger A, Ertürk A, Grathwohl SA, Neher JJ, Holtzman DM, Meyer-Luehmann M, Haass C. Nat Neurosci. 2019 Feb;22(2):191-204.

Links:

Alzheimer’s Disease and Related Dementias (National Institute on Aging/NIH)

Alzheimer’s Disease Neuroimaging Initiative (University of Southern California, Los Angeles)

Ewers Lab (University Hospital Munich, Germany)

Haass Lab (Ludwig-Maximilians-Universität München, Germany)

German Center for Neurodegenerative Diseases (Bonn)

Institute for Stroke and Dementia Research (Munich, Germany)

NIH Support: National Institute on Aging


The Brain Ripples Before We Remember

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Ripple brain
Credit: Thinkstock

Throw a stone into a quiet pond, and you’ll see ripples expand across the water from the point where it went in. Now, neuroscientists have discovered that a different sort of ripple—an electrical ripple—spreads across the human brain when it strives to recall memories.

In memory games involving 14 very special volunteers, an NIH-funded team found that the split second before a person nailed the right answer, tiny ripples of electrical activity appeared in two specific areas of the brain [1]. If the volunteer recalled an answer incorrectly or didn’t answer at all, the ripples were much less likely to appear. While many questions remain, the findings suggest that the short, high-frequency electrical waves seen in these brain ripples may play an unexpectedly important role in our ability to remember.

The new study, published in Science, builds on brain recording data compiled over the last several years by neurosurgeon and researcher Kareem Zaghloul at NIH’s National Institute of Neurological Disorders and Stroke (NINDS). Zaghloul’s surgical team often temporarily places 10-to-20 arrays of tiny electrodes into the brains of a people with drug-resistant epilepsy. As I’ve highlighted recently, the brain mapping procedure aims to pinpoint the source of a patient’s epileptic seizures. But, with a patient’s permission, the procedure also presents an opportunity to learn more about how the brain works, with exceptional access to its circuits.

One such opportunity is to explore how the brain stores and recalls memories. To do this, the researchers show their patient volunteers hundreds of pairs of otherwise unrelated words, such as “pencil and bishop” or “orange and navy.” Later, they show them one of the words and test their memory to recall the right match. All the while, electrodes record the brain’s electrical activity.

Previously published studies by Zaghloul’s lab [2, 3] and many others have shown that memory involves the activation of a number of brain regions. That includes the medial temporal lobe, which is involved in forming and retrieving memories, and the prefrontal cortex, which helps in organizing memories in addition to its roles in “executive functions,” such as planning and setting goals. Those studies also have highlighted a role for the temporal association cortex, another portion of the temporal lobe involved in processing experiences and words.

In their data collected in patients with epilepsy, Zaghloul’s team’s earlier studies had uncovered some telltale patterns. For instance, when a person correctly recalled a word pair, the brain showed patterns of activity that looked quite similar to those present when he or she first learned to make a word association.

Alex Vaz, one of Zaghloul’s doctoral students, thought there might be more to the story. There was emerging evidence in rodents that brain ripples—short bursts of high frequency electrical activity—are involved in learning. There was also some evidence in people that such ripples might be important for solidifying memories during sleep. Vaz wondered whether they might find evidence of ripples as well in data gathered from people who were awake.

Vaz’s hunch was correct. The reanalysis revealed ripples of electricity in the medial temporal lobe and the temporal association cortex. When a person correctly recalled a word pair, those two brain areas rippled at the same time.

Further analysis showed that the ripples appeared in those two areas a few milliseconds before a volunteer remembered a word and gave a correct answer. Your brain is working on finding an answer before you are fully aware of it! Those ripples also appear to trigger brain waves that look similar to those observed in the association cortex when a person first learned a word pair.

The finding suggests that ripples in this part of the brain precede and may help to prompt the larger brain waves associated with replaying and calling to mind a particular memory. For example, hearing the words, “The Fab Four” may ripple into a full memory of a favorite Beatles album (yes! Sgt. Pepper’s Lonely Hearts Club Band) or, if you were lucky enough, a memorable concert back in the day (I never had that chance).

Zaghloul’s lab continues to study the details of these ripples to learn even more about how they may influence other neural signals and features involved in memory. So, the next time you throw a stone into a quiet pond and watch the ripples, perhaps it will trigger an electrical ripple in your brain to remember this blog and ruminate about this fascinating new discovery in neuroscience.

References:

[1] Coupled ripple oscillations between the medial temporal lobe and neocortex retrieve human memory. Vaz AP, Inati SK, Brunel N, Zaghloul KA. Science. 2019 Mar 1;363(6430):975-978.

[2] Cued Memory Retrieval Exhibits Reinstatement of High Gamma Power on a Faster Timescale in the Left Temporal Lobe and Prefrontal Cortex. Yaffe RB, Shaikhouni A, Arai J, Inati SK, Zaghloul KA. J Neurosci. 2017 Apr 26;37(17):4472-4480.

[3] Human Cortical Neurons in the Anterior Temporal Lobe Reinstate Spiking Activity during Verbal Memory Retrieval. Jang AI, Wittig JH Jr, Inati SK, Zaghloul KA. Curr Biol. 2017 Jun 5;27(11):1700-1705.e5.

Links:

Epilepsy Information Page (National Institute of Neurological Disorders and Stroke/NIH)

Brain Basics (NINDS)

Zaghloul Lab (NINDS)

NIH Support: National Institute of Neurological Disorders and Stroke; National Institute of General Medical Sciences


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